Modern Science
According to the National Heart, Lung and Blood Institute, sleep is certainly needed, that too quality sleep for certain hours. 4-5 hours seems less to me.
It says --
Studies show that a good night's sleep improves learning. Whether you're learning math, how to play the piano, how to perfect your golf swing, or how to drive a car, sleep helps enhance your learning and problem-solving skills. Sleep also helps you pay attention, make decisions, and be creative.
Studies also show that sleep deficiency alters activity in some parts of the brain. If you're sleep deficient, you may have trouble making decisions, solving problems, controlling your emotions and behavior, and coping with change. Sleep deficiency also has been linked to depression, suicide, and risk-taking behavior.
Furthermore,
Sleep plays an important role in your physical health. For example, sleep is involved in healing and repair of your heart and blood vessels. Ongoing sleep deficiency is linked to an increased risk of heart disease, kidney disease, high blood pressure, diabetes, and stroke.
Sleep deficiency also increases the risk of obesity. For example, one study of teenagers showed that with each hour of sleep lost, the odds of becoming obese went up. Sleep deficiency increases the risk of obesity in other age groups as well.
The Guardian reports that less than six hours of sleep affect the genes. And, there are many drawbacks as well.
About celebs or known personalities sleeping 4 hours and working perfectly okay is considered as a myth!
WebMD, in its "7 Myths About Sleep" mentions...
Legendary short sleepers — including Bill Clinton, Madonna, and Margaret Thatcher — don't necessarily do better on fewer Zs. "They're just not aware of how sleepy they are," says Thomas Roth, Ph.D., sleep researcher at Henry Ford Hospital in Detroit. Too little sleep is bad for your health and your image: It can make you ineffective (it impairs performance, judgment, and the ability to pay attention), sick (it weakens your immune system), and overweight. In fact, women who slept five hours or less a night were a third more likely to gain 33 pounds or more over 16 years than women who slept seven hours, according to a Harvard Nurses' Health Study. Oddly, cutting too much sleep and getting less than six hours is associated with the same problems as sleeping too long: a higher risk of heart problems and death. And, of course, cheating on sleep hurts you behind the wheel: "Wakefulness for 18 hours makes you perform almost as though you're legally drunk," says Walsleben.
In an article on DailyMail.co.uk, it says that less than 6 hr of sleep increases the risks of having stroke even if you are fit and healthy. That said, those sleeping for less hours might look fit, but they are at the risks of something fatal.
[For those who believe only in evidences, the answer ends here]
[For those who believe more in traditional medicines, folk medicines and alternative medicines than researches, Ayurveda has an explanation]
Ayurvedic Aspect
There's something called 'satmya (saa-t-m-ya)'. In Ayurveda, it's described that if you start 'practicing' something with your body, your body 'gets adjusted' and it does not suffer the way others suffer with 'that practice'. In other words, I have been eating potatoes both the times for past 35 years AND it does not cause any harm to my body. It has become an integral part of my life and my body considers it as 'natural thing'.
Said that, if someone, right from his/her childhood or early adulthood has started practicing sleeping for a few hours, the body adjusts to it, and they find no problem with sleeping less as compared to those sleeping for 8 hrs regularly (from their childhood/early adulthood).
In my practice, I've seen people with more than 140 sugar, or 140/100 mmHg blood pressure with absolutely no signs of deteriorated health. While modern science finds it difficult to answer, Ayurveda says that the body has adjusted to whatsoever conditions it's living in.
